Fatty acids are one of the principal components of lipids. In vivo, fatty acids are bonded to glycerin via an ester bond to form lipids such as triacyiglycerol. Many animals and plants store and utilize fatty acids as an energy source. These fatty acids and lipids (fats and oils) stored in animals and plants are widely utilized for food or industrial use.
For example, higher alcohol derivatives that are obtained by reducing higher fatty acids having approximately 12 to 18 carbon atoms are used as surfactants. Alkyl sulfuric acid ester salts and alkylbenzenesurfonic acid salts are utilized as anionic surfactants, and polyoxyalkylene alkyl ethers, alkyl polyglycosides and the like are utilized as nonionic surfactants. These surfactants are used for detergents or disinfectants. As other higher alcohol derivatives, cationic surfactants such as alkylamine salts and mono- or dialkyl-quaternary amine salts are commonly used for fiber treatment agents, hair conditioning agents or disinfectants, and benzalkonium type quaternary ammonium salts are commonly used for disinfectants or antiseptics. Moreover, vegetable fats and oils are used also as raw materials of biodiesel fuels.
A fatty acid synthesis pathway of plants is localized in a chloroplast, in which an elongation reaction of a carbon chain is repeated starling from an acetyl-ACP (acyl-carrier-protein), and finally an acyl-ACP having 16 or 18 carbon atoms is synthesized. A β-ketoacyl-ACP synthase (β-ketoacyl-acyl-carrier-protein synthase: KAS) is an enzyme involved in control of chain length of an acyl group in the fatty acid synthesis pathway. In the plants, four kinds, namely KAS I, KAS II, KAS III and KAS IV are known to exist. KAS I to KAS IV are different in functions, respectively. KAS III functions in a stage of starting a chain length elongation reaction to elongate the acetyl-ACP having 2 carbon atoms to the acyl-ACP having 4 carbon atoms. In the subsequent elongation reaction, KAS I, KAS II and KAS IV are involved. KAS I is mainly involved in the elongation reaction to the palmitoyl-ACP having 16 carbon atoms, and KAS II is mainly involved in the elongation reaction to the stearoyl-ACP having 18 carbon atoms. On the other hand, it is believed that KAS IV is involved in the elongation reaction to medium chain acyl-ACP having 6 to 14 carbon atoms. KAS IV, in which less knowledge is obtained even in the plants, is considered to be KAS characteristic to the plants accumulating a medium chain fatty acid, such as Cuphea (Patent Literature 1, and Non-Patent Literature 1).
Recently, algae attract attention due to its usefulness in biofuel production. The algae can produce lipids that can be used as the biodiesel fuels through photosynthesis, and do not compete with foods. Therefore, the algae attract attention as next-generation biomass resources. Moreover, the algae are also reported to the effect mat the algae have higher lipid productivity and accumulation ability in comparison with plants. Research has started on a lipid synthesis mechanism of the algae and production technologies utilizing the mechanism, but unclear parts remain in many respects. Almost no report has been provided so far on the β-ketoacyl-ACP synthase of algae. In particular, no report has been made on KAS IV derived from the algae.